Embodiments described herein generally relate to downhole tools. More particularly, such embodiments relate to underreamers and stabilizers for enlarging the diameter of a wellbore.
In the drilling of oil and gas wells, concentric casing strings are installed and cemented in the wellbore as drilling progresses to increasing depths. Each new casing string is supported within the previously installed casing string, thereby limiting the annular area available outside the uppermost casing strings for the cementing operation. Further, as successively smaller diameter casing strings are suspended, the flow area for the production of oil and gas inside the casing strings decreases as the distance from the surface increases. Therefore, to increase the annular space for the cementing operation, and to increase the production flow area, it is often desirable to enlarge the diameter of the wellbore below the lower end portion of the previous casing string.
Underreamers are used for enlarging the diameter of the wellbore below the lower end portion of the previous casing string and stabilizers are used for controlling the trajectory of the underreamer during the drilling process. An underreamer generally has two states—an inactive or collapsed state where the cutters of the underreamer are stationary and the underreamer maintains a diameter small enough to pass through the existing casing strings, and an active or expanded state where one or more arms having the cutters on the end portions thereof extend radially outward from the underreamer. In the active state, the cutters are adapted to enlarge the diameter of the wellbore. As the underreamer is lowered into deeper and harder formations, however, additional underreamers may need to be deployed.
What is needed, therefore, are improved systems and methods for running multiple underreamers and/or stabilizers downhole.